This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-14214 filed on Jan. 23, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a starter motor for cranking an internal combustion engine. The starter motor includes a leaf spring for driving a pinion gear to a position engaging with a ring gear of the internal combustion engine.
2. Description of Related Art
Examples of starter motors having a leaf spring for driving a pinion gear into an engaging position with a ring gear of an internal combustion engine are disclosed in JPA-5-180131 and JP-A-50-65806. As shown in FIGS. 11A and 11B, in those conventional starter motors, it is quite common to insert one end of a leaf spring 200 into a square hole 120 formed in a connecting member 110 of a plunger 100. The plunger 100 and a pinion gear of a starter motor is operably connected via the leaf spring 200. Upon actuation of an electromagnetic actuator, a pinion gear of the starter motor is driven to a position engaging with a ring gear of an engine.
Since, in the conventional starter motor, the leaf spring 200 is connected to the plunger 100 by simply inserting one end of the leaf spring 200 into the square hole 120 as shown in FIG. 11B, the leaf spring 200 may be slantedly positioned in the square hole 120 as shown in FIG. 12, if the leaf spring 200 itself is slanted or the plunger 100 takes a slanted position in the electromagnetic actuator. When the slantedly positioned leaf spring 200 is driven by the plunger 100, the driving force is concentrated to a particular portion of the leaf spring 200, thereby making a life of the leaf spring 200 shorter.
Further, as shown in FIGS. 13A and 13B, a position where the leaf spring 200 contacts the square hole 120 changes during a course of a plunger actuation. Accordingly, a lever ratio of the leaf spring 200 (which is pivotally supported on a housing) cannot be maintained constant. As a result, there is a problem that a stable resilient force of the leaf spring 200 is not obtained.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved structure for coupling the leaf spring to the connecting member of the plunger, and thereby to prolong the life of the leaf spring and to obtain a stable resilient force of the leaf spring.
The pinion gear of the starter motor is driven to a position where the pinion gear engages with a ring gear of an internal combustion engine by a driving lever which is driven upon energization of an electromagnetic actuator. The electromagnetic actuator includes a plunger for driving the driving lever. The plunger has a connecting member to which a leaf spring of the driving lever is coupled. The pinion gear driven into engagement with the ring gear is further pushed toward the ring gear by a resilient force of the leaf spring connected to the driving lever.
An engaging portion is formed at one end of the leaf spring, and the engaging portion is coupled to an engaging surface of a square hole formed in the connecting member. The engaging surface is projected toward the engaging portion, forming a V-shape or a sphere-shape. Because the engaging surface is projected, the engaging portion of the leaf spring always contacts the engaging surface substantially at its center even if the leaf spring is not squarely positioned in the square hole of the connecting member.
The engaging portion of the leaf spring may be made by rounding or bending one end of the leaf spring, thereby forming a portion projected toward the engaging surface. The engaging portion may be made separately from the metallic leaf spring itself, using other materials such as resin. The separately made engaging portion may be shaped in a cylinder, a ball or the like, and it is connected to one end of the leaf spring. By coupling the engaging portion having the projection and the engaging surface having the projected surface, a driving force of the plunger is stably transferred to the leaf spring.
Preferably, the height of the projection formed on the engaging surface is made larger than a radius of rounded corners of the square hole, so that the engaging portion of the leaf spring adequately contacts the engaging surface, avoiding interference with the rounded corners. Further, the engaging portion of the leaf spring can be inserted into the square hole without making a gap in its width direction, thereby restricting rotation of the plunger in an inner bore of the electromagnetic actuator.
According to the present invention, the leaf spring and the plunger is adequately coupled so that the driving force of the plunger is uniformly applied to the leaf spring, thereby prolonging the life of the leaf spring. Further, a lever ratio of the driving lever is always maintained constant.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.